1. Field of the Invention
The invention relates to pivot shafts used in ventilator dampers. More particularly, the invention relates to a pivot shaft having an enclosed sleeve bearing and a closed end bushing.
2. State of the Art
Ventilation systems are controlled by dampers which open and close to regulate the flow of air through the system. A typical damper assembly 10 is shown in prior art FIG. 1 and includes a housing having a pair of sidewalls 12, 14 between which a plurality of vanes 16, 18 are pivotally mounted. The vanes 16, 18 are mounted to the sidewalls 12, 14 by pivot shafts or pins 20, 22, 24, 26 which are typically steel cylinders approximately three inches long and approximately one half inch in diameter. The pins are attached to the vanes by straps 28, 30, 32, 34 which are bolted to the vanes. The free end of each pin is inserted through a hole in one of the side walls as seen in prior art FIG. 2. For example, the free end of pin 22 is inserted through a bushing 23 which is held in a hole 15 in the sidewall 14. The vanes are thus mounted so that they may be rotated via a controlling arm 36 which is coupled to a motor (not shown) so that the damper can be opened or closed.
It is well known that dampers become jammed for a variety of reasons. Most commonly, dust and dirt which normally accumulates inside a ventilator system builds up around the pivot pins in the holes in the sidewalls of the damper assembly. This causes the pivotal joint to become frozen so that the vanes cannot be moved. Depending on the type of bushing used, the pivot joints can also freeze due to galling (metal to metal bonding) of the housing and/or bushing to the pin.
The failure of jammed dampers is a serious health and safety problem in large buildings which rely on a ventilator system in lieu of opening windows. For example, during the World Trade Center explosion, many people suffered from smoke inhalation because the building was not properly ventilated due to frozen dampers. In addition, what is now commonly known as "toxic building syndrome" or indoor air pollution is the direct result of frozen ventilator dampers.